Inking apparatuses of the type comprising a vibrator roller that is swung back and forth between an ink supply roller and an inking roller of an ink roller train in order to intermittently transfer ink from the ink supply roller to the inking roller are well-known as such in the art. Such ink apparatuses are in particular used in a variety of offset and letterpress printing presses used for commercial printing applications as well as for high security printing applications.
Inking apparatuses of the aforementioned type (and printing presses using the same) are in particular discussed in the “Handbook of Print Media/Technologies and Production Methods” (Helmut Kipphan, Springer-Verlag, 2001, ISBN 3-540-67326-1), Chapter 2.1.1.3, “Inking units” (pp. 213-217).
U.S. Pat. No. 4,509,424, U.S. Pat. No. 4,574,696, U.S. Pat. No. 4,584,939, U.S. Pat. No. 4,633,777, U.S. Pat. No. 4,640,189, U.S. Pat. No. 4,697,515, U.S. Pat. No. 4,766,809, U.S. Pat. No. 4,794,856, U.S. Pat. No. 5,007,339, U.S. Pat. No. 5,009,156, U.S. Pat. No. 5,036,763, U.S. Pat. No. 5,136,942, U.S. Pat. No. 6,101,939 for instance describe printing presses of the type comprising an offset printing group for the simultaneous recto-verso printing of a web or sheets as used for the production of security documents, in particular banknotes, which offset printing group comprises individual inking apparatuses of the above-mentioned type. In these particular instances, at least some of the individual inking apparatuses may include two separate ink ducts and vibrator rollers feeding inks to a same ink roller train. Two ink ducts are useful to ink a same printing plate with at least two different inks, which two different inks can furthermore be partially mixed in the axial direction to produce so-called iris (or rainbow) effects. Further examples of similar offset printing presses are disclosed in International Publications Nos. WO 2007/042919 A2, WO 2007/105059 A1, WO 2007/105061 A1, WO 2012/049610 A1, WO 2013/001518 A1, WO 2013/001009 A1, WO 2013/001010 A2 and WO 2014/056711 A1.
Letterpress printing presses, in particular numbering presses, as used for the production of security documents also typically make use of similar inking apparatuses with either one or two ink ducts. An example thereof is disclosed in International (PCT) Publication No. WO 2006/129245 A2.
Further examples of printing presses making use of vibrator-type inking apparatuses are known from European Patent Publications Nos. EP 0 444 227 A1, EP 1 149 699 A2, EP 1 319 509 A1, EP 1 738 907 A2 and Japanese Patent Applications Nos. JP 57-123062 A, JP 63-081045 A, JP 2000-062134 A.
FIGS. 1 and 2 illustrate a known sheet-fed offset printing press for simultaneous recto-verso printing of sheets of security documents as typically used for the production of banknotes, which printing press is designated globally by reference numeral 100. Such printing press is in particular marketed by the present Applicant under the product designation Super Simultan® IV. The basic configuration of this printing press is already described in International (PCT) Publication No. WO 2007/105059 A1, which publication is incorporated herein by reference in its entirety.
This printing press 100 comprises an offset printing group 101, which is specifically adapted to perform simultaneous recto-verso offset printing of the sheets and comprises, as is typical in the art, two blanket cylinders (or impression cylinders) 110, 120 (referenced in FIG. 2) rotating in the direction indicated by the arrows and between which the sheets are fed to receive multicolour impressions. In this example, blanket cylinders 110, 120 are three-segment cylinders which are supported between a pair of side frames designated by reference numeral 150. The blanket cylinders 110, 120 receive and collect different ink patterns in their respective colours from plate cylinders 115 and 125 (four on each side) which are distributed around a portion of the circumference of the blanket cylinders 110, 120. These plate cylinders 115 and 125, which each carry a corresponding printing plate PP, are themselves inked by corresponding inking apparatuses 10 and 20, respectively. The two groups of inking apparatuses 10, 20 are advantageously placed in two inking carriages 151, 152 that can be moved toward or away from the centrally-located plate cylinders 115, 125 and blanket cylinders 110, 120.
As is known in the art, each printing plate PP is wrapped around the corresponding plate cylinder 115, 125 and clamped at its leading end and trailing end by a suitable plate clamping system, which plate clamping system is located in a corresponding cylinder pit of the plate cylinder (see e.g. International (PCT) Publications Nos. WO 2013/001518 A1, WO 2013/001009 A1 and WO 2013/001010 A2).
Sheets are fed from a sheet feeding group 102 (including a feeder and feeder table) located next to the printing group 101 (on the right-hand side in FIGS. 1 and 2) to a succession of transfer cylinders 103a, 103b, 103c (three cylinders in this example) placed upstream of the blanket cylinders 110, 120. While being transported by the transfer cylinder 103b, the sheets may optionally receive a first impression on one side of the sheets using an additional printing group (not illustrated) as described for instance in U.S. Pat. No. 6,101,939 and International (PCT) Publication No. WO 2007/042919 A2, transfer cylinder 103b fulfilling the additional function of impression cylinder in such a case. In case the sheets are printed by means of the optional additional printing group, the sheets are first dried by a drying or curing unit 104 before being transferred to the blanket cylinders 110, 120 for simultaneous recto-verso printing.
In the example of FIGS. 1 and 2, the sheets are transferred onto the surface of blanket cylinder 120 where a leading edge of each sheet is held by appropriate gripper means located in cylinder pits between each segment of the blanket cylinder 120. Each sheet is thus transported by the blanket cylinder 120 to the printing nip between the blanket cylinders 110 and 120 where simultaneous recto-verso printing occurs. Once printed on both sides, the printed sheets are then transferred, as known in the art, to a chain gripper system 160 for delivery in a sheet delivery station 180 comprising multiple delivery pile units (three in this example).
In the example of FIGS. 1 and 2, first and second transfer cylinders (not referenced), such as suction drums or cylinders, are interposed between the chain gripper system 160 and the blanket cylinder 120. These first and second transfer cylinders are optional and designed to carry out inspection of the sheets on the recto and verso sides as described in International application No. WO 2007/105059 A1.
FIGS. 3 and 4 illustrate in greater detail one of the inking apparatuses 10, 20 of the printing press shown in FIGS. 1 and 2, namely the uppermost (fourth) inking apparatus 10 on the left-hand side of the printing press 100. While there are differences between the various inking apparatuses 10, 20 in terms of the arrangement and geometry of the relevant components thereof, all inking apparatuses 10, 20 have the same function and basically consist of the same essential elements. In that respect, as illustrated in FIG. 3, each inking apparatus 10, resp. 20, comprises two separate ink ducts 11, 12 supplying ink to an ink roller train 30 which in turns inks the printing plate PP carried by a corresponding one of the plate cylinders 115, resp. 125. More precisely, the ink ducts 11, 12 are both configured as ink fountain devices each comprising an ink supply roller (or duct roller) 13, resp. 14, cooperating with a vibrator roller 15, resp. 16, that is swung back and forth between the ink supply roller 13, resp. 14, and an inking roller 31 of the ink roller train 30. The vibrator rollers 15, 16 are typically made of a metallic inner core which is provided with an outer coating made e.g. of rubber, polymer or of any other material exhibiting suitable mechanical and ink-transfer properties.
In the example of FIGS. 1 to 4, the two vibrator rollers 15, 16 cooperate with one and a same inking roller 31 of the ink roller train 30. The inking apparatus could however be configured in such a way that the two vibrator rollers 15, 16 cooperate with distinct inking rollers of the ink roller train (see e.g. FIG. 16 where the two vibrator rollers 15, 16 respectively cooperate with a first inking roller 31* and a second inking roller 32* of the ink roller train 30*).
As further illustrated in FIG. 3, each inking apparatus 10, resp. 20, may optionally be configured for wet-offset printing, in which case a suitable dampening system 40 is provided to apply dampening solution onto the surface of a suitable wet-offset printing plate PP. In the case of dry-offset printing, the dampening system 40 is omitted, it being to be understood that dry-offset printing plates PP as used for the production of security documents are basically configured as letterpress printing plates with raised printing areas.
As further illustrated in FIG. 4, each ink duct 11, resp. 12 further comprises an ink fountain blade 11a, resp. 12a, that is adjusted with respect to the circumference of the relevant ink supply roller 13, resp. 14, so as to leave a determined spacing which defines the ink film thickness on the ink supply roller 13, resp. 14, i.e. the amount of ink that is transferred downstream to the vibrator roller 15, resp. 16, and then to the ink roller train 30 (or 30*), which spacing is typically adjustable. In such known inking apparatuses, adjustment of the spacing is typically carried out in individual ink zones by means of a number of ink keys that are distributed axially along the length of the corresponding ink supply roller and are individually adjustable.
In an inking apparatus of the aforementioned type, ink is fed intermittently from the relevant ink duct 11, resp. 12, via the vibrator roller 15, resp. 16. This vibrator roller 15, resp. 16, receives a relatively wide ink stripe from the corresponding ink supply roller 13, 14 and transfers part of this ink stripe to the inking roller 31 (resp. 31*, 32*) of the ink roller train 30 (resp. 30*).
In applications where a single ink duct and single vibrator roller are used, the vibrator roller typically exhibits a smooth and uniform outer surface. In contrast, in applications where two ink ducts and two vibrator rollers are used (as in the example of FIGS. 1 to 4), the vibrator rollers are typically structured in the axial direction so as to exhibit corresponding annular sections designed to transfer ink only in certain axially-distributed zones (see e.g. International (PCT) Publication No. WO 2014/056711 A1 or European Patent Publications Nos. EP 1 149 699 A2 and EP 1 738 907 A2).
The amount of ink transferred to the printing plate PP can be adjusted by means of each vibrator roller 15, resp. 16, namely by adjusting the frequency at which the vibrator roller 15, resp. 16, swings back and forth between the ink supply roller 13, resp. 14, and the inking roller 31 (resp. 31*, 32*), and/or by adjusting the amount of time (or “dwell”) the vibrator roller 15, resp. 16, runs in contact with the ink supply roller 13, resp. 14, thereby increasing the width/length of the relevant ink stripe in the circumferential direction.
In the known solutions, the amount of ink transferred to the printing plate is typically further adjusted by means a number of so-called ink keys provided at the extremity of the ink fountain blade, which ink keys are distributed along the axial length of the relevant ink supply roller to allow individual adjustment of the spacing between the ink fountain blade and the circumference of the ink supply roller. In the offset printing press of FIGS. 1 to 4, there are typically twenty-eight such ink keys, each having a width (along the axial direction) of the order of 30 mm. Each such ink key can be adjusted individually so as to alter the amount of ink in corresponding ink zones that are distributed along the axial direction of the relevant ink supply roller (see e.g. International (PCT) Publication No. WO 2012/049610 A1). Inking apparatuses using such ink zone systems are widely used in the art and are for instance marketed by Koenig & Bauer AG under the product designation ColorTronic.
In the context of the production of security documents, such as banknotes, individual sheets (or successive portions of a continuous web) are typically printed in such a way as to exhibit a matrix arrangement of repetitive imprints arranged in multiple columns and rows (m×n). FIG. 5 schematically illustrates a printed sheet S as used in the context of the production of banknotes and like security documents, which printed sheet S typically has a width W, in a direction x (hereinafter referred to as the “axial direction”) transversely to the path of the sheets S through the printing press as identified by the arrow in FIG. 5, of 820 mm and a length L, in a direction y (hereinafter referred to as the “circumferential direction” y) parallel to the path of the sheets S through the printing press, of 700 mm.
As already mentioned, the printed sheet S is printed so as to exhibit, within an effective printed area E, a matrix arrangement of multiple imprints P arranged side by side in multiple rows and columns. In the illustrated example, forty imprints P are printed in the effective printed area E in a matrix arrangement of eight (n=8) rows and five (m=5) columns, each imprint P exhibiting certain dimensions L1 (in the axial direction x) and L2 (in the circumferential direction y).
A limitation with the known inking apparatuses resides in the fact that the relevant arrangement and dimensions of the imprints P (which may vary from one case to another) do not precisely match the ink zone subdivision of the relevant inking apparatus, which ink zone subdivision is determined once and for all by the corresponding ink zone system. In particular, as soon as the length L1 of the imprints P differs from an integer multiple of the ink zone width, a mismatch between the ink zone subdivision and the relevant layout of imprints P occurs and ink key settings therefore need to be adjusted differently for each column of imprints P. This in turn means that an operator is faced with the task of finding appropriate ink key settings to adjust the inking in the relevant ink zones so that no major differences occurs in the inking between adjacent columns of imprints P, which adjustment process is time-consuming.
Furthermore, the operator is forced in practice to make compromises in the inking as it is not possible to adjust the inking independently and separately for each column of imprints P. Compromises in particular have to be made in the regions where two adjacent columns of imprints P meet. This is schematically illustrated by FIG. 6 which illustrates adjacent (columns of) imprints P, P′, P″ and an illustrative ink zone subdivision (with ink zones ZA to ZK) that does not precisely match the length L1 of the imprints P, P′, P″, it being to be understood that the ink zone subdivision thus differs from one column of imprints P, P′, P″ to another.
In that respect, considering for instance a pattern A within the column of imprints P, the ink key settings for ink zones ZD and ZE where the pattern A is located are necessarily different from the ink key settings for ink zones ZJ and ZK where the same pattern A is located in the adjacent column of imprints P′. The same is true with respect to pattern B within the column of imprints P which is covered by three ink zones in this illustrative example, namely ink zones ZG to ZI and the same pattern B within the adjacent column of imprints P″ which is covered by four ink zones, namely ink zones ZA to ZD.
In practice, with the known solutions, it is not therefore possible to achieve an optimum inking of the relevant printing plates and obtain an optimal printed result. Furthermore, finding the best possible ink settings takes considerable time which negatively affects production costs and efficiency.
There is therefore a need for an improved solution.